Arc chute for air circuit breaker

ABSTRACT

The arc chute of low-voltage air magnetic type electric circuit breaker comprises a stack of spaced-apart steel plates. Some of the plates are coated with ceramic insulating material on their uppermost regions and are located between groups of the uncoated plates to increase the electrical breakdown path and inhibit flashover at the upper end of the arc chute where exhaust gases are hottest.

Feb. 8, 1972 S N mm WT mA mm mm m .m 0 Mn m T m @N wG u 0 9F 2 4 3 2 [54] ARC CHUTE FOR AIR CIRCUIT BREAKER [72] Inventors: Charles H. Armitage, Wauwatosa, Wis; 4

Henry L. Peek wenesley; Herbert M. 560,257 3/19 4 Great Bnta1n......................200/l47B Pflanz, Westwood, both of Mass.

Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Jan. 8, 1970 Primary Examiner-Robert S. Macon Attorney-Thomas F. Kirby, Lee H. Kaiser and Robert B. Benson [73] Assignee:

[57] ABSTRACT The are chute of low-voltage air magnetic type electric circuit [22] Filed:

[211 App]. No.:

breaker comprises a stack of spaced-apart steel plates. Some of the plates are coated with ceramic insulating material on 200/144 200/ l 47 B their uppermost regions and are located between groups of the 33/08 uncoated plates to increase the electrical breakdown path and .200/ 144, 147 147 inhibit flashover at the upper end of the arc chute where exhaust gases are hottest.

[52] US. Cl. [51] Int. [58] Field of 2 Claims, 2 Drawing Figures References Cited UNITED STATES PATENTS 2,147,419 2/1939 Baker.................................200/147B I Q Q Q Q ARC CI-IUTE FOR AIR CIRCUIT BREAKER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to are chute for electric circuit breakers and, particularly, to those which employ a plurality of spaced-apart plates to divide up an are into smaller segments during extinguishment.

2. Description of the Prior Art Some of the circuit breakers for interrupting alternating current use an arc chute having a stack of spaced-apart metal plates located between a pair of arc runners and adjacent, usually above, the circuit breaker contacts. Such arc chutes divide the long are between the arc runners into a multiplicity of series connected smaller arcs as it moves through the arc chute; the object being to raise the reignition voltage of the arc to a level which permanently exceeds the recovery voltage. Extinguishment is aided by the cooling of the small arcs in contact with the metal plates and by the turbulence present as the arcs move through the spaces between the metal plates.

To prevent the are from reigniting after passing through the stack of plates, it has been the practice to place plates made of solid insulating material in coplanar edgewise relationship with the top edge of some or all of the metal plates. However, in order for this alone to be completely effective there must be a close tolerance fit between the edges of the metal plates and the insulating plates. Plates made of solid insulating material have also been interspersed between pairs or groups of the metal plates to aid arc extinguishment by providing a more tortuous path for the are. US. Pat. No. 3,296,402, issued Jan. 3, 1967, to G, J. Meinders illustrates the foregoing approach. US. Pat. No. 2,91 1,505, issued Nov. 3, 1959, to D. Legg et a]. teaches an arrangement wherein all plates in the arc chute are made of solid sheets of magnetizable metal and completely covered or coated with two different types of insulating material. In any event, both of these approaches and the use of insulating plates in various arrangements with metal plates to aid in arc extinguishment, while achieving the desired electrical result, very often result in more costly, complicated and fragile arc chutes. It is desirable, therefore, to provide new and improved arc chutes wherein the plates are constructed and arranged so as to improve the extinguishing ability of the arc chute while at the same time reducing the number and cost of parts otherwise required and simplifying manufacturing operations.

SUMMARY OF THE INVENTION The present invention contemplates an arc chute wherein a stack or plurality of spaced-apart plates, preferably made of magnetizable material, are disposed between a pair of arc runners and wherein, after the arc has moved through the stack, flashover or reignition of the arc across the top of the stack is likely to occur. In accordance with the present invention it is proposed to coat some of the metal plates with are resistance refractory insulating material, such as ceramic, at their uppermost regions and to intersperse the coated plates with the uppermost regions and to intersperse the coated plates with the uncoated metal plates in new preferred arrangements to prevent flashover and to increase the length of the arc path in hotter regions of the arc chute but to use such coated plates in conjunction with the rest of the plates in the stack only insofar as necessary so that as many metal plates as possible can be retained in the stack to give the voltage drop necessary to provide higher are voltage.

OBJECTS OF THE INVENTION It is an object of the present invention to provide an improved arc chute which employs a combination of metal plates and insulating plates partially coated with refractory insulating material to effect arc extinguishment and prevent restriking of the are.

Another object is to provide an arc chute of the aforesaid character which provided an elongated path for the arc and inhibits restriking of the arc across the top of the stack of plates.

Another object is to provide an arc chute which avoids close tolerance fitting between dissimilar constitutent elements to effect efficient arc extinguishment.

Another object is to provide an arc chute which employs plates which are of uniform size and configuration but which are readily coated so as to provide an arc chute which has advantages of metal and insulating plates in combination.

Another object is to provide an arc chute of the aforesaid character which is economical to fabricate and reliable in use.

Other objects and advantages will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing illustrates a preferred embodiment of the invention but it is to be understood that the embodiment illustrated is susceptible of modifications with respect to details thereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 is a side elevational view, partly in section, of a portion of a circuit breaker arc chute incorporating the present invention; and

FIG. 2 is a view taken along line II--II of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 of the drawing, the numerals l0 and 12 designate a stationary and movable contact, respectively, of an electric circuit breaker which separate to establish an arc. An arc chute 14 is associated with contacts 10 and 12 and comprises a pair of spaced-apart sidewalls I6 and 18 which are made of electrical insulating material such as ceramic, fiber, or the like. It is to be understood that the sidewalls l6 and 18 are mirror images of each other and are formed with suitable projections and recesses to support various components therein when the sidewalls are fastened together. The sidewalls l6 and 18 define an arcing chamber 20 in the lower portion of the arc chute 14 wherein stationary contact 10 and movable contact I2 are disposed. Stationary contact 10 is rigidly mounted with respect to arc chute l4 and is located at one end of chamber 20. Stationary contact I0 is electrically connected to a first stationary electrically conductive arc runner 22 which is also located at the aforesaid one end'of chamber 20 of arc chute 14. Movable contact 12 is pivotally mounted for clockwise and counterclockwise movement (with respect to FIG. I) within chamber 20 of arc chute 14 into an out of engagement, respectively, with stationary contact 10. When movable contact 12 is moved counterclockwise it comes into proximity with a second stationary electrically conductive arc runner 24 which is located at the other end of chamber 20 of arc chute 14 and spaced apart from are runner 22. During circuit interruption, an arc established between the contacts 10 and 12 is transferred therefrom so that it becomes established between the are runners 22 and 24 and travels upward thereon, as hereinafter explained.

Arc chute 14 comprises a stack 26 of plates which span the sidewalls l6 and 18 above chamber 20 and are disposed in spaced-apart relationship between the arc runners 22 and 24. One end of the stack of plates 26 is closer to the contacts than the other end. Arc chute 14 is provided with means for cooling the exhaust gases expelled from the top of the stack of plates 26. Such means take the form of hollow baffle members 42 which aresupported by perforated insulating means 44.

All plates in stack 26 are of the same configuration and size and may be assumed to be made of magnetizable material such as copper-plated steel. The plates in stack 26 are arranged with respect to each other so that the upper edges of all plates (the edges most remote from the contacts) terminate in a first common horizontal plane. The upper edges of the arc runners 22 and 24 also terminate in or below the aforesaid first plane. The lower edges of all plates in stack 26 (the edges nearest the contacts) terminate in a second common horizontal plane. The plates in stack 26 are held in position by entrapment in grooves 30 provided in the sidewalls l6 and 18. Each plate in' stack 26 is provided with a triangular slot 28 at its lower edge to guide the are into the stack of plates during operation of the are chute.

in accordance with the invention the plates designated by the numerals 32, 34, 36, 38 and 40 are each provided near their upper ends, i.e., the regions thereof most remote from the contacts 10 and 12, with a coating of ceramic insulating material which is applied by spraying or dipping and firing. In the embodiment shown, there are two uncoated plates intervening between the plates 32 and 34, between plates 34 and 36, between plates 36 and 38, and between plates 38 and 40. The spacing between each plate and an adjacent plate in the stack is regular and is the same as the spacing between the arc runners 22 and 2d and the plates adjacent thereto. ln effect, the uncoated plates in the stack are arranged in groups which are separated from each other by a coated plate, as shown in FIG. 5. in the embodiment shown, each group comprises two uncoated plates, except the last group nearest runner 22 which comprises only one plate.

l lashovcr of the are at the upper end of the stack 26 is el fcctivcly prevented by coated plates arranged as shown. The arrangement of coated plates also requires a more tortuous path for the are as it meets the lower edges of the coating on the plates and begins to move up the stack.

Arc chute 14 operates as follows: Assume that the contacts l and H. of the circuit breaker are closed and the current is flowing thcrcthrough. As movable contact 12 is moved counterclockwise (with respect to HO. 1 from closed toward open position an arc appears between contacts and 12. Because of electromagnetic forces present. the terminal point of the are on contact ll) transfers to are runner 22 and the terminal point of the are on contact 12 moves to the extreme tip of contact 12. The are forms an inverted U-shape with its highest point entering within the slots 28 in the stack of plates 26 at the end of the stack nearest arc runner 22. As movable con tact 12 moves closer to are runner 24, the arc terminal on the former transfers to the latter, and an elongated arc is established between the are runners 22 and 24. As the elongated arc moves up through and past the slots 28 in the stack 26, it is divided into a plurality of series-related small arcs. The small arcs tend to move upward through the stack at a relatively uniform rate. In the embodiment shown, the arcing forces and arc byproducts are most numerous at the end of the arc chute nearest stationary contact 10 (i.e., the point of arc initiation). Since the arcing forces and byproducts are less effective at the upper end of the stack, the insulated plates thereat are sufficient to reduce the likelihood of flashover across the top of the plates. However, these factors are offset to some extent because during interruption of an arc, the hot gas from arcing is vented through the arc chute in an upward direction. As a result of cool air or gas entering from the bottom a temperature gradient exists along the vertical path of the arc chute. The hot gas in the upper zone has a lower breakdown voltage than the cooler gas in the lower zone. Nevertheless, as the arcs move further through the stack they are prevented from flashing over the top edges of the plates in the stack by the coating of insulation on the plates 32, 34, 36, 38 and 40 for several reasons. First. as the small are between each uncoated plate and its adjacent coated plate hits the edge of the coating its upward travel is slowed. This slowing of the are at several points has the effect of elongating the arc and further increasing its voltage. Secondly, the coated plates tend to reduce the likelihood of llashovcr across the top of the metal plates because they increase the distance the arc must travel. Thus, the breakdown path is effectively increased and strikeover prevented by an arc chute in accordance with the invention.

As previously mentioned. it is desirable to retain as. many metal plates as possible in the stack in order to increase the are voltage. The use of coated metal plates permits this. Exhaust products from the are are cooled and condensed by means of the baffles 42 before being expelled from the arc chute.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In combination in a low-voltagc air magnetic type electric circuit breaker,

a pair of contacts between which an arc is established upon separation, a pair of spaced-apart arc runners to which said are is transf erred from said contacts, and a stack of spaced-apart plates located between said pair ofarc runners, 7 all of said plates in said stack comprising a flat single sheet of magnetizable material and being of the same size and configuration and having their top edges aligned in the same plane, each sheet having front and rear surfaces and top, bottom and side edge surfaces, at least one but not all of said sheets in said stack having all surfaces of at least the upper one-third portion thereof remote from said contacts coated with a single'layer of refractory are resistant electrical insulating material to provide a coated plate, said stack of plates comprising a plurality of groups of uncoated plates,

each group being separated from an adjacent group by one coated plate. 2. A combination according to claim 1 wherein each of said groups comprises two plates. 

1. In combination in a low-voltage air magnetic type electric circuit breaker, a pair of contacts between which an arc is established upon separation, a pair of spaced-apart arc runners to which said arc is transferred from said contacts, and a stack of spaced-apart plates located between said pair of arc runners, all of said plates in said stack comprising a flat single sheet of magnetizable material and being of the same size and configuration and having their top edges aligned in the same plane, each sheet having front and rear surfaces and top, bottom and side edge surfaces, at least one but not all of said sheets in said stack having all surfaces of at least the upper one-third portion thereof remote from said contacts coated with a single layer of refractory arc resistant electrical insulating material to provide a coated plate, said stack of plates comprising a plurality of groups of uncoated plates, each group being separated from an adjacent group by one coated plate.
 2. A combination according to claim 1 wherein each of said groups comprises two plates. 